Prevention of sludge formation in lubricating oils



Patented Nov. 3, 1936 FFICE PREVENTION OF SLUDGE FORMATION IN LUBRICATING OILS Elliott Alfred Evans, London, England, assignor to C. C. Wakefield & Company Limited, London, England, a British company No Drawing.

Application November 22, 1934,

Serial No. 754,283. 'In Great Britain December 3 Claims.

It is well known that lubricating oils, when exposed to high temperature conditions in the presence of oxygen, tend to deteriorate owing to the formation in the oil of gummy substances which interfere with the lubricating properties of the oil. This deterioration is most pronounced in the lubrication of the pistons of internal- .combustion engines, where the gummy substances become embedded in the piston-ringgrooves, thus impairing the sealing of the cylinder gases, and causing rapid breakdown of the engine or deterioration of its performance. It is found that the formation of sludge and gummy substances in lubricating oils, when used in in- 5 ternal-combustion engines, 'is at least partly due to oxidation of the oils promoted by the catalytic effect of the iron in the walls of the engine cylinders.

According to this invention, there is provided a lubricant for use in internal-combustion engines having ferrous metal cylinders, which lubricant comprises a lubricating oil having dispersed therein one or more substances of a class which counteracts the catalytic action of the ferrous metal upon the oil. This class of materials includes organic compounds of chromium and organic compounds of tin. Other suitable organo-metallic compounds may readily be determined by carrying out oxidation tests on the oil in the presence of iron.

Sludge or gummy substances may also be produced in the oil by direct oxidation quite apart from the aforesaid catalytic action, and the anticatalyst itself may not have the property of preventing such direct oxidation. A feature of this invention therefore consists in dispersing in the lubricating oil, in addition to an anticatalyst, a small proportion of a substance for counteracting the aforesaid direct oxidation. 0 Various substances are already known to possess this property, such as tin compounds; thus, according to this invention there may be dispersed in the oil'bpth a small proportion of an organic compound of chromium and a small proportion of an organic compound of tin. It is indicated above that tin is included in the class of material which counteracts the catalytic action of the ferrous metal upon the oil. It, however,

possesses this propertiy to a lesser degree than D chromium, but it is a good anti-oxidant.

Another cause of deterioration of the lubricating oil is due to spontaneous ignition or cracking'of the oil under high temperature and pressure conditions.

Preferably, the lubricating oil has dispersed therein both a small proportion of a substance for counteracting the aforesaid action of metallic surfaces on the oil, for example a small proportion of chromium or its compounds, and a small proportion of a sludge-preventing substance, such as tin or its compounds, and a small proportion of a substance for raising the temperature at which spontaneous ignition or cracking of the 011 takes place, for example tetra-ethyl lead or other suitable lead compounds.

The invention includes within its scope a lubricant comprising a lubricating oil having dispersed therein in addition to a small proportion of an organic compound of chromium either a small proportion of an organic compound of tin, or of an organic compound of lead, or both said latter substances.'

Preferably, oil-soluble compounds of the above metals are selected, such as chromium oleate, tin oleate and tetra-ethyl lead, which substances may be added to the oil in proportions of up to 1% by weight of each compound, according to the nature of the lubricating oil treated. For example, it has been found by experiment that when added to a compounded oil in the proportion of .1% tin oleate, 5% chromium oleate and .l% tetra-ethyl lead, the tendency to gum-formation in the oil when used in intemal-combustion engines was considerably reduced.

It has been found. however, that with certain oils, the use of all three metallic compounds is not necessary; thus, a mixture of chromium and tin compounds may be used, or, alternatively, a mixture of an oil-soluble chromium compound and an oil-soluble lead compound may be beneficial. For example, in a paraflinic mineral oil, we have found that the addition to the oil of .4% chromium oleate and .l% tin oleate gave beneficial results in reducing the gum-formation in the oil when used in an internal-combustion engine. With a naphthenic oil a similar advantage has been observed in reducing gum-formation by the addition to the oil of .5% chromium oleate and .l% tetra-ethyl lead.

It has been found that owing to the widely different chemicalcompositions of individual lubricating oils, it is preferable to treat each oil according to its particular composition and although advantage may be gained by the addition of one substance to any given lubricating oil, an enhanced eiiect may be obtained by the addition in the proper proportions of the mixtures of various metallic substances herein mineral lubricating oil having dispersed thereproposed. in material amounts up to .4%"'chromium oleate I claim:- and up .1% tin oleate. 1. A lubricant comprising a mineral lubricat- 3. A lubricant comprising a lubricating oil 5 ing oil having dispersed therein material having dispersed therein in material amounts 5 amounts up to .4% chromium oleate, up to up to .4% chromium oleate and up to .1% tin .1% tin oleate and up to .1% tetra-ethyl lead. oleate.

2. A lubricant comprising a. parafilnic ELLIOTT ALFRED EVANS. 

